Tilney L G, DeRosier D J
Dev Biol. 1986 Jul;116(1):119-29. doi: 10.1016/0012-1606(86)90048-5.
In 8-day-old embryos stereocilia can be identified on the hair cells of the chick cochlea; within each is a small population of actin filaments which extend from the tip of the stereocilium to the apical cytoplasm of the cell. These filaments are not ordered in a regular way, however, and tend to be found near the lateral margins of the stereocilia with large spaces between adjacent filaments. By 9 days the spaces between adjacent filaments are reduced and there are regions where the crossover points of adjacent actin helices are in register even though in cross section the actin filaments do not lie on a regular lattice. By 10-11 days the actin filaments become progressively more crossbridged together and we can recognize in longitudinal section horizontal stripes caused by the periodicity of the crossbridges. In transverse section the filaments begin to lie on a hexagonal lattice. Each stereocilium, however, contains less than 100 actin filaments. Evidence is presented that once crossbridging is maximal and the filaments hexagonally packed (Days 11-12), the stereocilia increase in width by the orderly addition of actin filaments to the lateral margins of the existing filament bundle so that by Day 16 we find up to 400 filaments all packed on a hexagonal lattice. Thus there are two stages in bundle formation. In the first a small number of filaments condense into a hexagonally packed, crosslinked bundle. In the second, the bundle increases in diameter by addition of filaments to the periphery of the bundle in a process akin to crystal growth. From observations on the elongation of filaments in the rootlets and stereocilia, we conclude that rootlets grow by addition of subunits at the nonpreferred end while stereocilia elongate by addition to the preferred end. What makes this interesting is that these two modes of addition occur at different developmental times.
在8日龄胚胎的鸡耳蜗毛细胞上可识别出静纤毛；每个静纤毛内有一小群肌动蛋白丝，从静纤毛尖端延伸至细胞顶端细胞质。然而，这些丝没有规则排列，往往在静纤毛的侧缘附近发现，相邻丝之间有很大间隙。到9日龄时，相邻丝之间的间隙减小，存在相邻肌动蛋白螺旋交叉点对齐的区域，尽管在横切面上肌动蛋白丝并不位于规则晶格上。到10 - 11日龄时，肌动蛋白丝逐渐更多地相互交联，我们在纵切面上可以识别出由交联周期性引起的水平条纹。在横切面上，丝开始排列成六边形晶格。然而，每个静纤毛含有的肌动蛋白丝少于100根。有证据表明，一旦交联达到最大且丝呈六边形排列（11 - 12日龄），静纤毛通过向现有丝束的侧缘有序添加肌动蛋白丝而增宽，以至于到16日龄时，我们发现多达400根丝都排列在六边形晶格上。因此，束形成有两个阶段。第一阶段，少量丝凝聚成六边形排列、交联的束。第二阶段，束通过在束周边添加丝而直径增大，这一过程类似于晶体生长。从对小根和静纤毛中丝伸长的观察，我们得出结论，小根通过在非优选端添加亚基而生长，而静纤毛通过在优选端添加而伸长。有趣的是，这两种添加方式发生在不同的发育时期。
